/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Predicates.alwaysTrue;
import static com.google.common.base.Predicates.equalTo;
import static com.google.common.base.Predicates.in;
import static com.google.common.base.Predicates.not;
import static com.google.common.collect.Maps.safeContainsKey;
import static com.google.common.collect.Maps.safeGet;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Function;
import com.google.common.base.Predicate;
import com.google.common.base.Supplier;
import com.google.common.collect.Maps.IteratorBasedAbstractMap;
import com.google.common.collect.Maps.ViewCachingAbstractMap;
import com.google.common.collect.Sets.ImprovedAbstractSet;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.j2objc.annotations.WeakOuter;
import java.io.Serializable;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.Spliterator;
import java.util.Spliterators;
import javax.annotation.Nullable;

/**
 * {@link Table} implementation backed by a map that associates row keys with column key / value
 * secondary maps. This class provides rapid access to records by the row key alone or by both keys,
 * but not by just the column key.
 *
 * <p>
 * The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *
 * <p>
 * Lookups by row key are often faster than lookups by column key, because the data is stored in a
 * {@code Map<R, Map<C, V>>}. A method call like {@code
 * column(columnKey).get(rowKey)} still runs quickly, since the row key is provided. However,
 * {@code column(columnKey).size()} takes longer, since an iteration across all row keys occurs.
 *
 * <p>
 * Note that this implementation is not synchronized. If multiple threads access this table
 * concurrently and one of the threads modifies the table, it must be synchronized externally.
 *
 * @author Jared Levy
 */
@GwtCompatible
class StandardTable<R, C, V> extends AbstractTable<R, C, V> implements Serializable {
    @GwtTransient
    final Map<R, Map<C, V>> backingMap;
    @GwtTransient
    final Supplier<? extends Map<C, V>> factory;

    StandardTable(Map<R, Map<C, V>> backingMap, Supplier<? extends Map<C, V>> factory) {
        this.backingMap = backingMap;
        this.factory = factory;
    }

    // Accessors

    @Override
    public boolean contains(@Nullable Object rowKey, @Nullable Object columnKey) {
        return rowKey != null && columnKey != null && super.contains(rowKey, columnKey);
    }

    @Override
    public boolean containsColumn(@Nullable Object columnKey) {
        if (columnKey == null) {
            return false;
        }
        for (Map<C, V> map : backingMap.values()) {
            if (safeContainsKey(map, columnKey)) {
                return true;
            }
        }
        return false;
    }

    @Override
    public boolean containsRow(@Nullable Object rowKey) {
        return rowKey != null && safeContainsKey(backingMap, rowKey);
    }

    @Override
    public boolean containsValue(@Nullable Object value) {
        return value != null && super.containsValue(value);
    }

    @Override
    public V get(@Nullable Object rowKey, @Nullable Object columnKey) {
        return (rowKey == null || columnKey == null) ? null : super.get(rowKey, columnKey);
    }

    @Override
    public boolean isEmpty() {
        return backingMap.isEmpty();
    }

    @Override
    public int size() {
        int size = 0;
        for (Map<C, V> map : backingMap.values()) {
            size += map.size();
        }
        return size;
    }

    // Mutators

    @Override
    public void clear() {
        backingMap.clear();
    }

    private Map<C, V> getOrCreate(R rowKey) {
        Map<C, V> map = backingMap.get(rowKey);
        if (map == null) {
            map = factory.get();
            backingMap.put(rowKey, map);
        }
        return map;
    }

    @CanIgnoreReturnValue
    @Override
    public V put(R rowKey, C columnKey, V value) {
        checkNotNull(rowKey);
        checkNotNull(columnKey);
        checkNotNull(value);
        return getOrCreate(rowKey).put(columnKey, value);
    }

    @CanIgnoreReturnValue
    @Override
    public V remove(@Nullable Object rowKey, @Nullable Object columnKey) {
        if ((rowKey == null) || (columnKey == null)) {
            return null;
        }
        Map<C, V> map = safeGet(backingMap, rowKey);
        if (map == null) {
            return null;
        }
        V value = map.remove(columnKey);
        if (map.isEmpty()) {
            backingMap.remove(rowKey);
        }
        return value;
    }

    @CanIgnoreReturnValue
    private Map<R, V> removeColumn(Object column) {
        Map<R, V> output = new LinkedHashMap<R, V>();
        Iterator<Entry<R, Map<C, V>>> iterator = backingMap.entrySet().iterator();
        while (iterator.hasNext()) {
            Entry<R, Map<C, V>> entry = iterator.next();
            V value = entry.getValue().remove(column);
            if (value != null) {
                output.put(entry.getKey(), value);
                if (entry.getValue().isEmpty()) {
                    iterator.remove();
                }
            }
        }
        return output;
    }

    private boolean containsMapping(Object rowKey, Object columnKey, Object value) {
        return value != null && value.equals(get(rowKey, columnKey));
    }

    /** Remove a row key / column key / value mapping, if present. */
    private boolean removeMapping(Object rowKey, Object columnKey, Object value) {
        if (containsMapping(rowKey, columnKey, value)) {
            remove(rowKey, columnKey);
            return true;
        }
        return false;
    }

    // Views

    /**
     * Abstract set whose {@code isEmpty()} returns whether the table is empty and whose
     * {@code clear()} clears all table mappings.
     */
    @WeakOuter
    private abstract class TableSet<T> extends ImprovedAbstractSet<T> {
        @Override
        public boolean isEmpty() {
            return backingMap.isEmpty();
        }

        @Override
        public void clear() {
            backingMap.clear();
        }
    }

    /**
     * {@inheritDoc}
     *
     * <p>
     * The set's iterator traverses the mappings for the first row, the mappings for the second row,
     * and so on.
     *
     * <p>
     * Each cell is an immutable snapshot of a row key / column key / value mapping, taken at the
     * time the cell is returned by a method call to the set or its iterator.
     */
    @Override
    public Set<Cell<R, C, V>> cellSet() {
        return super.cellSet();
    }

    @Override
    Iterator<Cell<R, C, V>> cellIterator() {
        return new CellIterator();
    }

    private class CellIterator implements Iterator<Cell<R, C, V>> {
        final Iterator<Entry<R, Map<C, V>>> rowIterator = backingMap.entrySet().iterator();
        Entry<R, Map<C, V>> rowEntry;
        Iterator<Entry<C, V>> columnIterator = Iterators.emptyModifiableIterator();

        @Override
        public boolean hasNext() {
            return rowIterator.hasNext() || columnIterator.hasNext();
        }

        @Override
        public Cell<R, C, V> next() {
            if (!columnIterator.hasNext()) {
                rowEntry = rowIterator.next();
                columnIterator = rowEntry.getValue().entrySet().iterator();
            }
            Entry<C, V> columnEntry = columnIterator.next();
            return Tables.immutableCell(rowEntry.getKey(), columnEntry.getKey(), columnEntry.getValue());
        }

        @Override
        public void remove() {
            columnIterator.remove();
            if (rowEntry.getValue().isEmpty()) {
                rowIterator.remove();
            }
        }
    }

    @Override
    Spliterator<Cell<R, C, V>> cellSpliterator() {
        return CollectSpliterators
                .flatMap(backingMap.entrySet().spliterator(),
                        (Map.Entry<R, Map<C, V>> rowEntry) -> CollectSpliterators.map(
                                rowEntry.getValue().entrySet().spliterator(),
                                (Map.Entry<C, V> columnEntry) -> Tables.immutableCell(rowEntry.getKey(),
                                        columnEntry.getKey(), columnEntry.getValue())),
                        Spliterator.DISTINCT | Spliterator.SIZED, size());
    }

    @Override
    public Map<C, V> row(R rowKey) {
        return new Row(rowKey);
    }

    class Row extends IteratorBasedAbstractMap<C, V> {
        final R rowKey;

        Row(R rowKey) {
            this.rowKey = checkNotNull(rowKey);
        }

        Map<C, V> backingRowMap;

        Map<C, V> backingRowMap() {
            return (backingRowMap == null || (backingRowMap.isEmpty() && backingMap.containsKey(rowKey)))
                    ? backingRowMap = computeBackingRowMap()
                    : backingRowMap;
        }

        Map<C, V> computeBackingRowMap() {
            return backingMap.get(rowKey);
        }

        // Call this every time we perform a removal.
        void maintainEmptyInvariant() {
            if (backingRowMap() != null && backingRowMap.isEmpty()) {
                backingMap.remove(rowKey);
                backingRowMap = null;
            }
        }

        @Override
        public boolean containsKey(Object key) {
            Map<C, V> backingRowMap = backingRowMap();
            return (key != null && backingRowMap != null) && Maps.safeContainsKey(backingRowMap, key);
        }

        @Override
        public V get(Object key) {
            Map<C, V> backingRowMap = backingRowMap();
            return (key != null && backingRowMap != null) ? Maps.safeGet(backingRowMap, key) : null;
        }

        @Override
        public V put(C key, V value) {
            checkNotNull(key);
            checkNotNull(value);
            if (backingRowMap != null && !backingRowMap.isEmpty()) {
                return backingRowMap.put(key, value);
            }
            return StandardTable.this.put(rowKey, key, value);
        }

        @Override
        public V remove(Object key) {
            Map<C, V> backingRowMap = backingRowMap();
            if (backingRowMap == null) {
                return null;
            }
            V result = Maps.safeRemove(backingRowMap, key);
            maintainEmptyInvariant();
            return result;
        }

        @Override
        public void clear() {
            Map<C, V> backingRowMap = backingRowMap();
            if (backingRowMap != null) {
                backingRowMap.clear();
            }
            maintainEmptyInvariant();
        }

        @Override
        public int size() {
            Map<C, V> map = backingRowMap();
            return (map == null) ? 0 : map.size();
        }

        @Override
        Iterator<Entry<C, V>> entryIterator() {
            final Map<C, V> map = backingRowMap();
            if (map == null) {
                return Iterators.emptyModifiableIterator();
            }
            final Iterator<Entry<C, V>> iterator = map.entrySet().iterator();
            return new Iterator<Entry<C, V>>() {
                @Override
                public boolean hasNext() {
                    return iterator.hasNext();
                }

                @Override
                public Entry<C, V> next() {
                    return wrapEntry(iterator.next());
                }

                @Override
                public void remove() {
                    iterator.remove();
                    maintainEmptyInvariant();
                }
            };
        }

        @Override
        Spliterator<Entry<C, V>> entrySpliterator() {
            Map<C, V> map = backingRowMap();
            if (map == null) {
                return Spliterators.emptySpliterator();
            }
            return CollectSpliterators.map(map.entrySet().spliterator(), this::wrapEntry);
        }

        Entry<C, V> wrapEntry(final Entry<C, V> entry) {
            return new ForwardingMapEntry<C, V>() {
                @Override
                protected Entry<C, V> delegate() {
                    return entry;
                }

                @Override
                public V setValue(V value) {
                    return super.setValue(checkNotNull(value));
                }

                @Override
                public boolean equals(Object object) {
                    // TODO(lowasser): identify why this affects GWT tests
                    return standardEquals(object);
                }
            };
        }
    }

    /**
     * {@inheritDoc}
     *
     * <p>
     * The returned map's views have iterators that don't support {@code remove()}.
     */
    @Override
    public Map<R, V> column(C columnKey) {
        return new Column(columnKey);
    }

    private class Column extends ViewCachingAbstractMap<R, V> {
        final C columnKey;

        Column(C columnKey) {
            this.columnKey = checkNotNull(columnKey);
        }

        @Override
        public V put(R key, V value) {
            return StandardTable.this.put(key, columnKey, value);
        }

        @Override
        public V get(Object key) {
            return StandardTable.this.get(key, columnKey);
        }

        @Override
        public boolean containsKey(Object key) {
            return StandardTable.this.contains(key, columnKey);
        }

        @Override
        public V remove(Object key) {
            return StandardTable.this.remove(key, columnKey);
        }

        /**
         * Removes all {@code Column} mappings whose row key and value satisfy the given predicate.
         */
        @CanIgnoreReturnValue
        boolean removeFromColumnIf(Predicate<? super Entry<R, V>> predicate) {
            boolean changed = false;
            Iterator<Entry<R, Map<C, V>>> iterator = backingMap.entrySet().iterator();
            while (iterator.hasNext()) {
                Entry<R, Map<C, V>> entry = iterator.next();
                Map<C, V> map = entry.getValue();
                V value = map.get(columnKey);
                if (value != null && predicate.apply(Maps.immutableEntry(entry.getKey(), value))) {
                    map.remove(columnKey);
                    changed = true;
                    if (map.isEmpty()) {
                        iterator.remove();
                    }
                }
            }
            return changed;
        }

        @Override
        Set<Entry<R, V>> createEntrySet() {
            return new EntrySet();
        }

        @WeakOuter
        private class EntrySet extends ImprovedAbstractSet<Entry<R, V>> {
            @Override
            public Iterator<Entry<R, V>> iterator() {
                return new EntrySetIterator();
            }

            @Override
            public int size() {
                int size = 0;
                for (Map<C, V> map : backingMap.values()) {
                    if (map.containsKey(columnKey)) {
                        size++;
                    }
                }
                return size;
            }

            @Override
            public boolean isEmpty() {
                return !containsColumn(columnKey);
            }

            @Override
            public void clear() {
                removeFromColumnIf(alwaysTrue());
            }

            @Override
            public boolean contains(Object o) {
                if (o instanceof Entry) {
                    Entry<?, ?> entry = (Entry<?, ?>) o;
                    return containsMapping(entry.getKey(), columnKey, entry.getValue());
                }
                return false;
            }

            @Override
            public boolean remove(Object obj) {
                if (obj instanceof Entry) {
                    Entry<?, ?> entry = (Entry<?, ?>) obj;
                    return removeMapping(entry.getKey(), columnKey, entry.getValue());
                }
                return false;
            }

            @Override
            public boolean retainAll(Collection<?> c) {
                return removeFromColumnIf(not(in(c)));
            }
        }

        private class EntrySetIterator extends AbstractIterator<Entry<R, V>> {
            final Iterator<Entry<R, Map<C, V>>> iterator = backingMap.entrySet().iterator();

            @Override
            protected Entry<R, V> computeNext() {
                while (iterator.hasNext()) {
                    final Entry<R, Map<C, V>> entry = iterator.next();
                    if (entry.getValue().containsKey(columnKey)) {
                        @WeakOuter
                        class EntryImpl extends AbstractMapEntry<R, V> {
                            @Override
                            public R getKey() {
                                return entry.getKey();
                            }

                            @Override
                            public V getValue() {
                                return entry.getValue().get(columnKey);
                            }

                            @Override
                            public V setValue(V value) {
                                return entry.getValue().put(columnKey, checkNotNull(value));
                            }
                        }
                        return new EntryImpl();
                    }
                }
                return endOfData();
            }
        }

        @Override
        Set<R> createKeySet() {
            return new KeySet();
        }

        @WeakOuter
        private class KeySet extends Maps.KeySet<R, V> {
            KeySet() {
                super(Column.this);
            }

            @Override
            public boolean contains(Object obj) {
                return StandardTable.this.contains(obj, columnKey);
            }

            @Override
            public boolean remove(Object obj) {
                return StandardTable.this.remove(obj, columnKey) != null;
            }

            @Override
            public boolean retainAll(final Collection<?> c) {
                return removeFromColumnIf(Maps.<R>keyPredicateOnEntries(not(in(c))));
            }
        }

        @Override
        Collection<V> createValues() {
            return new Values();
        }

        @WeakOuter
        private class Values extends Maps.Values<R, V> {
            Values() {
                super(Column.this);
            }

            @Override
            public boolean remove(Object obj) {
                return obj != null && removeFromColumnIf(Maps.<V>valuePredicateOnEntries(equalTo(obj)));
            }

            @Override
            public boolean removeAll(final Collection<?> c) {
                return removeFromColumnIf(Maps.<V>valuePredicateOnEntries(in(c)));
            }

            @Override
            public boolean retainAll(final Collection<?> c) {
                return removeFromColumnIf(Maps.<V>valuePredicateOnEntries(not(in(c))));
            }
        }
    }

    @Override
    public Set<R> rowKeySet() {
        return rowMap().keySet();
    }

    private transient Set<C> columnKeySet;

    /**
     * {@inheritDoc}
     *
     * <p>
     * The returned set has an iterator that does not support {@code remove()}.
     *
     * <p>
     * The set's iterator traverses the columns of the first row, the columns of the second row,
     * etc., skipping any columns that have appeared previously.
     */
    @Override
    public Set<C> columnKeySet() {
        Set<C> result = columnKeySet;
        return (result == null) ? columnKeySet = new ColumnKeySet() : result;
    }

    @WeakOuter
    private class ColumnKeySet extends TableSet<C> {
        @Override
        public Iterator<C> iterator() {
            return createColumnKeyIterator();
        }

        @Override
        public int size() {
            return Iterators.size(iterator());
        }

        @Override
        public boolean remove(Object obj) {
            if (obj == null) {
                return false;
            }
            boolean changed = false;
            Iterator<Map<C, V>> iterator = backingMap.values().iterator();
            while (iterator.hasNext()) {
                Map<C, V> map = iterator.next();
                if (map.keySet().remove(obj)) {
                    changed = true;
                    if (map.isEmpty()) {
                        iterator.remove();
                    }
                }
            }
            return changed;
        }

        @Override
        public boolean removeAll(Collection<?> c) {
            checkNotNull(c);
            boolean changed = false;
            Iterator<Map<C, V>> iterator = backingMap.values().iterator();
            while (iterator.hasNext()) {
                Map<C, V> map = iterator.next();
                // map.keySet().removeAll(c) can throw a NPE when map is a TreeMap with
                // natural ordering and c contains a null.
                if (Iterators.removeAll(map.keySet().iterator(), c)) {
                    changed = true;
                    if (map.isEmpty()) {
                        iterator.remove();
                    }
                }
            }
            return changed;
        }

        @Override
        public boolean retainAll(Collection<?> c) {
            checkNotNull(c);
            boolean changed = false;
            Iterator<Map<C, V>> iterator = backingMap.values().iterator();
            while (iterator.hasNext()) {
                Map<C, V> map = iterator.next();
                if (map.keySet().retainAll(c)) {
                    changed = true;
                    if (map.isEmpty()) {
                        iterator.remove();
                    }
                }
            }
            return changed;
        }

        @Override
        public boolean contains(Object obj) {
            return containsColumn(obj);
        }
    }

    /**
     * Creates an iterator that returns each column value with duplicates omitted.
     */
    Iterator<C> createColumnKeyIterator() {
        return new ColumnKeyIterator();
    }

    private class ColumnKeyIterator extends AbstractIterator<C> {
        // Use the same map type to support TreeMaps with comparators that aren't
        // consistent with equals().
        final Map<C, V> seen = factory.get();
        final Iterator<Map<C, V>> mapIterator = backingMap.values().iterator();
        Iterator<Entry<C, V>> entryIterator = Iterators.emptyIterator();

        @Override
        protected C computeNext() {
            while (true) {
                if (entryIterator.hasNext()) {
                    Entry<C, V> entry = entryIterator.next();
                    if (!seen.containsKey(entry.getKey())) {
                        seen.put(entry.getKey(), entry.getValue());
                        return entry.getKey();
                    }
                } else if (mapIterator.hasNext()) {
                    entryIterator = mapIterator.next().entrySet().iterator();
                } else {
                    return endOfData();
                }
            }
        }
    }

    /**
     * {@inheritDoc}
     *
     * <p>
     * The collection's iterator traverses the values for the first row, the values for the second
     * row, and so on.
     */
    @Override
    public Collection<V> values() {
        return super.values();
    }

    private transient Map<R, Map<C, V>> rowMap;

    @Override
    public Map<R, Map<C, V>> rowMap() {
        Map<R, Map<C, V>> result = rowMap;
        return (result == null) ? rowMap = createRowMap() : result;
    }

    Map<R, Map<C, V>> createRowMap() {
        return new RowMap();
    }

    @WeakOuter
    class RowMap extends ViewCachingAbstractMap<R, Map<C, V>> {
        @Override
        public boolean containsKey(Object key) {
            return containsRow(key);
        }

        // performing cast only when key is in backing map and has the correct type
        @SuppressWarnings("unchecked")
        @Override
        public Map<C, V> get(Object key) {
            return containsRow(key) ? row((R) key) : null;
        }

        @Override
        public Map<C, V> remove(Object key) {
            return (key == null) ? null : backingMap.remove(key);
        }

        @Override
        protected Set<Entry<R, Map<C, V>>> createEntrySet() {
            return new EntrySet();
        }

        @WeakOuter
        class EntrySet extends TableSet<Entry<R, Map<C, V>>> {
            @Override
            public Iterator<Entry<R, Map<C, V>>> iterator() {
                return Maps.asMapEntryIterator(backingMap.keySet(), new Function<R, Map<C, V>>() {
                    @Override
                    public Map<C, V> apply(R rowKey) {
                        return row(rowKey);
                    }
                });
            }

            @Override
            public int size() {
                return backingMap.size();
            }

            @Override
            public boolean contains(Object obj) {
                if (obj instanceof Entry) {
                    Entry<?, ?> entry = (Entry<?, ?>) obj;
                    return entry.getKey() != null && entry.getValue() instanceof Map
                            && Collections2.safeContains(backingMap.entrySet(), entry);
                }
                return false;
            }

            @Override
            public boolean remove(Object obj) {
                if (obj instanceof Entry) {
                    Entry<?, ?> entry = (Entry<?, ?>) obj;
                    return entry.getKey() != null && entry.getValue() instanceof Map
                            && backingMap.entrySet().remove(entry);
                }
                return false;
            }
        }
    }

    private transient ColumnMap columnMap;

    @Override
    public Map<C, Map<R, V>> columnMap() {
        ColumnMap result = columnMap;
        return (result == null) ? columnMap = new ColumnMap() : result;
    }

    @WeakOuter
    private class ColumnMap extends ViewCachingAbstractMap<C, Map<R, V>> {
        // The cast to C occurs only when the key is in the map, implying that it
        // has the correct type.
        @SuppressWarnings("unchecked")
        @Override
        public Map<R, V> get(Object key) {
            return containsColumn(key) ? column((C) key) : null;
        }

        @Override
        public boolean containsKey(Object key) {
            return containsColumn(key);
        }

        @Override
        public Map<R, V> remove(Object key) {
            return containsColumn(key) ? removeColumn(key) : null;
        }

        @Override
        public Set<Entry<C, Map<R, V>>> createEntrySet() {
            return new ColumnMapEntrySet();
        }

        @Override
        public Set<C> keySet() {
            return columnKeySet();
        }

        @Override
        Collection<Map<R, V>> createValues() {
            return new ColumnMapValues();
        }

        @WeakOuter
        class ColumnMapEntrySet extends TableSet<Entry<C, Map<R, V>>> {
            @Override
            public Iterator<Entry<C, Map<R, V>>> iterator() {
                return Maps.asMapEntryIterator(columnKeySet(), new Function<C, Map<R, V>>() {
                    @Override
                    public Map<R, V> apply(C columnKey) {
                        return column(columnKey);
                    }
                });
            }

            @Override
            public int size() {
                return columnKeySet().size();
            }

            @Override
            public boolean contains(Object obj) {
                if (obj instanceof Entry) {
                    Entry<?, ?> entry = (Entry<?, ?>) obj;
                    if (containsColumn(entry.getKey())) {
                        // The cast to C occurs only when the key is in the map, implying
                        // that it has the correct type.
                        @SuppressWarnings("unchecked")
                        C columnKey = (C) entry.getKey();
                        return get(columnKey).equals(entry.getValue());
                    }
                }
                return false;
            }

            @Override
            public boolean remove(Object obj) {
                if (contains(obj)) {
                    Entry<?, ?> entry = (Entry<?, ?>) obj;
                    removeColumn(entry.getKey());
                    return true;
                }
                return false;
            }

            @Override
            public boolean removeAll(Collection<?> c) {
                /*
                 * We can't inherit the normal implementation (which calls Sets.removeAllImpl(Set,
                 * *Collection*) because, under some circumstances, it attempts to call
                 * columnKeySet().iterator().remove, which is unsupported.
                 */
                checkNotNull(c);
                return Sets.removeAllImpl(this, c.iterator());
            }

            @Override
            public boolean retainAll(Collection<?> c) {
                checkNotNull(c);
                boolean changed = false;
                for (C columnKey : Lists.newArrayList(columnKeySet().iterator())) {
                    if (!c.contains(Maps.immutableEntry(columnKey, column(columnKey)))) {
                        removeColumn(columnKey);
                        changed = true;
                    }
                }
                return changed;
            }
        }

        @WeakOuter
        private class ColumnMapValues extends Maps.Values<C, Map<R, V>> {
            ColumnMapValues() {
                super(ColumnMap.this);
            }

            @Override
            public boolean remove(Object obj) {
                for (Entry<C, Map<R, V>> entry : ColumnMap.this.entrySet()) {
                    if (entry.getValue().equals(obj)) {
                        removeColumn(entry.getKey());
                        return true;
                    }
                }
                return false;
            }

            @Override
            public boolean removeAll(Collection<?> c) {
                checkNotNull(c);
                boolean changed = false;
                for (C columnKey : Lists.newArrayList(columnKeySet().iterator())) {
                    if (c.contains(column(columnKey))) {
                        removeColumn(columnKey);
                        changed = true;
                    }
                }
                return changed;
            }

            @Override
            public boolean retainAll(Collection<?> c) {
                checkNotNull(c);
                boolean changed = false;
                for (C columnKey : Lists.newArrayList(columnKeySet().iterator())) {
                    if (!c.contains(column(columnKey))) {
                        removeColumn(columnKey);
                        changed = true;
                    }
                }
                return changed;
            }
        }
    }

    private static final long serialVersionUID = 0;
}
